We propose to use selected mutants and recombinant DNA's to study two objectives related to tRNA function: 1) Plasmids containing tRNA genes are being combined in vitro to produce new species of tRNA in vivo in order to study the effects of tRNA sequence on function. Some tRNA mutants are being used for the same purposes. 2) Partially synthetic tRNA genes, made by assembling the DNA products of organochemically derived DNA and sections of natural genes are being tested for translational activity on the ribosome.